1. Field of the Invention
The present invention relates to brake devices, and in particular to anti-lock brake devices having a pump operable to pump a working liquid. The pump transfers the working liquid from a reservoir to which the working liquid was previously discharged from a brake cylinder. The pump discharges the working liquid to the hydraulic circuit on the side of a master cylinder.
2. Description of the Related Art
In general, a brake device comprises a master cylinder and a brake cylinder. The master cylinder serves to supply a working liquid to a brake cylinder in response to the operation of a brake pedal. The pressure of the working liquid operates the brake cylinder in order to press a brake pad(s) against a braking surface. Brake devices are known that incorporate an anti-lock device that functions so as to prevent one or more wheels from being accidentally locked (halted in rotation while the vehicle is still moving) during the braking operation. This type of brake device is typically equipped with a reservoir, a pump, and a solenoid valve. The reservoir serves to accumulate the working fluid (liquid) discharged from a brake cylinder during the activation of the anti-lock system. The working liquid is discharged in order to reduce the hydraulic pressure within the brake cylinder for one or more wheels. The pump serves to move the working liquid from the reservoir and discharge the working liquid to the hydraulic circuit on the side of the master cylinder. A reciprocation pump, such as a plunger pump, is typically used as the pump for this purpose. The solenoid valve is operated in order to relieve or apply hydraulic pressure within the brake cylinder. Such brake devices are disclosed in Japanese laid-Open Patent Publication No. 8-230642 and U.S. Pat. No. 6,000,764.
However, the reciprocating pump may produce a pulsation in pressure as the working liquid is discharged from the pump. When such pulsation (pressure variation) is produced, various pipelines as well as the master cylinder of the brake device may vibrate and possibly generate noises. In order to reduce the pulsation or fluctuation of the hydraulic pressure of the working liquid produced by the pump, there has been proposed to provide a buffer chamber in the communication path of the hydraulic circuit between the pump and the master cylinder. However, it has been difficult to sufficiently reduce the pulsation by merely incorporating a buffer chamber.